The question would be asked: "Why did Bhishma, Dronacharya, and Vidura not desert the evil company of king Dhritarashtra and join the Pandavas?"
The answer to this query is being searched for all these centuries, in India and elsewhere! In part, the answer is given by Bhishma himself. He had vowed to remain loyal to the throne of Hastinapur irrespective of who occupied it. This pledge was more than anything to him. His life, non-righteous behavior of Kauravas, and sufferings of Pandavas had no value in face of his pledge.
As to Dronacharya and Vidura, they were the paid servants of king Dhritarashtra. It was essential for them to serve their master who gave them name, fame, and position. To oppose the king or to find faults with him (or his sons) was not the culture of that time. Probably, they had no say in such matters; and to revolt was to show disloyalty to the throne 'whose salt they had eaten'.
Today also we see many officers, secretaries, and servants loyal to corrupt rulers and head of the states! We see many 'righteous persons' keeping mum over irregularities and misconduct of their 'bosses'. This even includes President of America, the most prosperous, progressive, democratic and free nation state. Watergate, and ... How many of the righteous officers and secretaries resign? Almost none! If this is the case of USA, it is better not to talk about less developed countries of Latin America, Africa, and Asia.
The question of Bhishma, Dronacharya, Vidura, etc. remaining silent at the great injustice meted out to Draupadi and Pandavas will always remain unanswered.
Such incidences are not uncommon in any era or epoch. Some are dramatized, others are forgotten in the flow of time. However, they expose weakness of human nature -character. Individually, we may learn from them to rise above uncivilized behavior, but any attempt to totally 'eliminate such tendencies from the society' is bound to come to naught!
Very slowly, indeed after many centuries, the effect will show in more civilized state of human existence, I agree.